1. Field of the Invention
The invention relates to a method and apparatus for aerobic decomposition of organic waste matter in a composting vessel.
2. Discussion of the Prior Art
It is known to compost organic waste material, such as sludge from a waste water treatment facility, utilizing mechanical composting bins or vessels which circulate aeration air through the organic matter to be composted. The goal is to produce a nonodorous organic material which can often be sold as a soil amendment or land fill and which is at least not costly or objectionable to dispose of. The composting will also tend to reduce the amount of water in the organic matter, resulting in drying of the material to further alleviate disposal problems.
The usual approach to mechanical composting has involved the use of upright, cylindrical devices in the nature of silos, through which pressurized aeration air is circulated to aid in the decomposition process. Such vertical silos have certain disadvantages, such as excessive compaction of lower layers of material which has been vertically stacked as well as complicated mechanical equipment with high power consumption.
Horizontal composting methods and equipment have been proposed as alternatives to vertical composting silos. Horizontal composting has the advantage of a simple construction in which organic matter is moved horizontally along the length of the composting vessel in a stepwise fashion with the use of a hydraulically actuated ram. Aeration air is circulated through the horizontal vessel to aid in carrying out the composting process in a relatively short period of time. Such a method and apparatus is disclosed in U.S. Pat. Nos. 4,384,877 and 4,436,817 to Nemetz, whioh U.S. patents are hereby incorporated herein by reference.
Although horizontal composting methods and equipment have represented a substantial advance in the art in that they avoid unduly compacted layers of organic matter while at the same time providing very simple and economical-to-operate equipment, it has been found that even further control over the extent of compaction of the organic matter without adding substantially to the complexity or operating costs of the equipment would be desirable. Such control over the extent of compaction could, in turn, result in control over the temperature of the aeration air circulated through the organic matter during composting. By controlling the temperature of aeration air, the need for cooling or, sometimes, heating of the aeration air can be avoided. This, in turn, avoids the need for expensive cooling or heating equipment and the high energy costs associated with the use of such equipment over a long period of time. In this regard, both the temperature and the pressure of he aeration air are interrelated, in that increased pressure of the aeration air results in an increased temperature of that air. Controlling the extent of compaction of the organic material controls the pressure required for effecting circulation of the air through the organic material to, in turn, control its temperature.
Another area for which a need for improvement has arisen involves the nozzles or orifices through which the aeration air flows during the composting process. Since the organic matter rests over the orifices in known arrangements, there is a tendency for the organic matter to enter the orifices and clog them. This is particularly so when the orifices are under suction. Thus, it becomes desireable to avoid this clogging tendency in a expedient manner.